Over at Wired, CalTech planetary sciences researcher Jeffrey Marlow has a great post about what happens to plants when they grow in the weightless conditions of the International Space Station. Though there are changes in their metabolisms, the plants turn out basically just the way they would on Earth. Marlow concludes:

What's perhaps even more surprising than these metabolic shifts is the ability of plants to withstand weightlessness with relative ease: the seedlings still grew, and they still looked a lot like plants. The apparent fact that a trait like gravity, which has dominated the entire experience of life on Earth, has not become a requirement for life, is remarkable.

Remarkable, indeed. It sounds like plants can hold up in space better than humans can.